Plasma arc torches are widely used in the cutting and marking of materials. A plasma arc torch generally includes an electrode and a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). The torch produces a plasma arc, i.e., a constricted ionized jet of a gas with high temperature and high momentum. Gases used in the torch can be non-reactive (e.g., argon or nitrogen) or reactive (e.g., oxygen or air). During operation, a pilot arc is first generated between the electrode (part of the cathode) and the nozzle (part of the anode). Generation of the pilot arc can be by means of a high frequency, high voltage signal coupled to a DC power supply and the torch or by means of any of a variety of starting methods. Plasma arc torches can utilize cartridges including one or more consumable components (e.g., a nozzle, electrode, and/or a swirl ring) for ease of installation and operation.
FIGS. 1 and 2 show a cartridge for a plasma arc torch 100 having a nozzle 104, a shield 108, an electrode 112, a retaining cap 116, a swirl ring 120, and a fixed “crown” or contact element 124 disposed about the swirl ring 120. This contact element 124 does not move relative to the swirl ring 120, e.g., is fixed in an axial direction relative to the swirl ring 120. The contact element 124 passes a cutting current from a plunger 132 of the plasma arc torch 100 to the electrode 112. Because plasma cutting requires a high cutting current, a solid electrical connection must be maintained between the plasma arc torch 100 and the electrode 112 to ensure proper operation and to limit or eliminate arcing, which can damage equipment and shorten component life.
This “fixed crown” design has a failure mode when the contact element 124 is not in full contact with the plunger 132 (e.g., because the cartridge is not fully tightened within the plasma arc torch 100). In this failure mode, a gap 228 can be created between the contact element 124 and the plunger 132, as shown in FIG. 2. This gap 228 results in a poor electrical connection, and can cause poor performance and component failure. In addition, the poor connection can lead to arcing between the cathode (e.g., the plunger 132) and the contact element 124, which can destroy the entire torch instead of just one or more consumable components. What is needed is a consumable cartridge that avoids this failure mode and ensures proper and complete contact between the plunger 132 and the contact element 124, even if the cartridge is not fully screwed on or is otherwise loose.